Data storage device

ABSTRACT

A data storage device for storing digital information in a readable form is described made up of one or more memory elements, each memory element comprising a planar magnetic conduit capable of sustaining and propagating a magnetic domain wall formed into a continuous propagation track. Each continuous track is provided with at least one and preferably a large number of inversion nodes whereat the magnetization direction of a domain wall propagating along the conduit under action of a suitable applied field, such as a rotating magnetic field, is changed.

BACKGROUND

1. Technical Field

The examples of embodiments relate to a data storage device for thestorage of digital information such as computer files, digital music,digital video etc., and, in particular, to a data storage device towhich data can be written and read back an unlimited number of times.

2. Description of Related Art

A wide range of data storage devices has become available in recentyears employing a range of media for a range of digital data storageapplications. Data storage devices are designed which are adapted tosome of a variety of operational characteristics, including capacity,speed of access, write/rewrite ability, ability to retain data stablyover time (with or without power), size, robustness, portability and thelike.

Known data storage devices include magnetic tape storage, magnetic harddisk storage, and optical disk storage. All offer advantages of goodstorage capacity and relatively rapid data access, and all can beadapted for ready write and rewrite of data. All require moving parts inthe form of electromechanical or optical readers. This can limit theextent to which devices incorporating such data storage media can beminiaturized, and limit the use of the device in high-vibrationenvironments. Although in each case the surface medium is the key todata storage, the mechanisms involved require careful control ofproperties also of any supporting substrate. Thus, such devices have tobe of carefully controlled construction. Moreover all require the readerto have access to the surface of the device, which can place limitationson design freedom for the device.

SUMMARY

It is an object of the examples of embodiments to provide an alternativedigital data storage device which offers versatility in alternativesituations, in particular for example which can be miniaturized, and/orwhich can be incorporated into other devices such as smart cards,identification tags and patches or the like, and/or which can beincorporated onto flexible substrates, and/or which can be used inhigh-vibration environments, and/or which is of simple/low costmanufacture etc.

It is a particular object of the examples of embodiments to provide adata storage device which compactly and effectively stores digital dataand provides for data to be written to the device and read back anunlimited number of times.

Thus, according to examples of embodiments, a data storage device forstoring digital information (such as computer files, digital music,digital video, etc.) in a readable form comprises one or more, and inparticular a plurality of, memory elements, each memory elementcomprising a planar magnetic conduit capable of sustaining andpropagating a magnetic domain wall formed into a continuous propagationtrack, wherein each continuous track is provided with at least one andoptionally a plurality and in particular a large number of inversionnodes whereat the magnetization direction of a domain wall propagatingalong the conduit under action of a suitable applied field is changedand in particular substantially reversed.

Each conduit is formed into a continuous propagation track. Convenientlya conduit is formed into a closed loop to comprise such a continuouspropagation track. Such a loop is provided with at least one andoptionally a plurality and in particular a large number of inversionnodes. Data is able to pass around the closed loop in accordance withthe mechanism outlined below. In a variant, the magnetic conduit doesnot form an entire closed loop of inversion nodes, but rather a linearchain of inversion nodes with means to transfer data between the twoends thereof so that data is still able to circulate around anapparently closed loop, for example comprising a data writing facilityat one end of the chain and data reading facility at the other end ofthe chain, and additional circuitry to feed the data back electronicallyfrom the output of the chain to the input of the chain.

Conveniently the inversion nodes comprise features in the structure andshape of the conduit which are so adapted as to cause a change in themagnetization direction, and preferably a substantial reversal in themagnetization direction, of a domain propagating thereacross underaction of a suitable applied field, such as a directionally varying andin particular a rotating magnetic field.

It is nevertheless necessary that the conduit direction and hence thedomain wall propagation direction varies without sharp discontinuitiesat any point. Thus, the conduit in the region of and comprising theinversion node must have configurational features such as to cause achange in the magnetization direction, and preferably a substantialreversal in the magnetization direction, of a domain propagatingthereacross but without any specific sharp variation in propagationdirection.

In a preferred embodiment, an inversion node comprises a substantialreversal of magnetization direction at the inversion node. Preferably,the inversion node comprises a portion in which a direction change awayfrom the initial path and a subsequent direction change back to theinitial path are provided in the conduit such that no direct propagationpath is possible across the deviating portion. In particular, deviationscomprise 90° deviations from the initial path. For the reasonsindicated, deviations from the initial path preferably occur graduallyover a distance along the conduit track.

For example, the inversion node comprises a cycloidal portion within theconduit loop structure, in particular directed internally, or atopological equivalent of such a structure.

Preferably, a plurality of such cycloidal portions are provided in eachloop. Thus a device in accordance with the examples of embodimentspreferably comprises a number of magnetic conduits formed into closedloops each comprising a plurality of cycloids serving to effect abruptdirectional reversals in a magnetization direction of a domain wallpassing thereacross and hence serving as inversion points for domainwalls as they are propagated along the conduit of the device by asuitable driving field.

Preferably, each cycloid has a turning radius which is in the range ofthree to ten times the conduit width. Preferably, the cycloid is such asto produce a substantial change, for example a substantial 180°reversal, of magnetization direction as a domain wall passestherethrough.

In accordance with the present data storage device, the magnetic conduitneeds to have architecture capable of sustaining and propagating adomain wall under action of a controlling field. Typically, the magneticconduit may be formed as a continuous track of magnetic material. Thus,the loops in the device preferably comprise magnetic wires, inparticular generally planar magnetic wires on a suitable substrate.

The data storage device thus uses a number of planar magnetic conduitsand in particular magnetic wires which are preferably shaped into closedloops of cycloids. In particular, the device employs magnetic nanoscaletechnology, the device comprising a number of planar magnetic nanowirespreferably formed into a plurality of closed loops of cycloids.

The planar magnetic nanowires are preferably less than 1 μm in width andare formed onto any suitable substrate. Width is a tradeoff between theimproved storage capacity of devices employing narrower nanoscale wiresand fabrication costs and complexities. However, devices incorporatingwires above one micron are unlikely to be effective, and 50 nm is alikely practical lower limit of cost-effective practicality for currentwire forming techniques. It should be emphasized that it is not atechnical effect limit, and that improved fabrication techniques couldrender further miniaturized data storage devices in accordance withexamples of embodiments practical.

The wires are deposited on a substrate in the form of a thin layer ofmagnetic material. Wire thickness is optimized for optimum performanceof the device, and is broadly a function of width. In particular, wirethickness is generally around 1/40th of wire width. Wire thickness isgenerally not less than 2 nm, and preferably not less than 3 nm. Wiresare in practice unlikely to be more than 25 nm thick.

The wires can be fabricated by optical lithography, X-ray lithography,micro-contact printing, e-beam lithography, deposition through a shadowmask or by some other suitable method. The wires are made from amagnetic material such as Permalloy (Ni₈₀Fe₂₀) or CoFe or some othersoft magnetic material.

The data storage device incorporating inversion nodes as described aboveis subject to the application of a suitable directionally varying and inparticular rotating magnetic field in a manner of operation described ingreater detail below, which gives the inversion node a memory function.The provision of a plural array of loops each incorporating one or moreinversion nodes allows a device in accordance with examples ofembodiments to store data serially in a ring.

Data can be written to a device in accordance with examples ofembodiments and read back an unlimited number of times. Unlike magnetictape storage or magnetic hard disk storage, the present data storagedevice requires no moving parts. Consequently, it can be easilyminiaturized and used in high-vibration environments. The principle ofthe present data storage device is very simple, and manufacturing costscan be kept low. Moreover, no power is required to retain data in thememory of the present data storage device when it is not in use.

The present data storage device uses a number of magnetic conduits suchas planar magnetic wires. The planar wires are formed on some substrate,but unlike microelectronic memory, this substrate plays no role in theelectronic or magnetic operation of the device, serving essentially onlyto provide mechanical support. Conventional silicon substrates may stillbe used, but since no functionality is necessary from the substrate,materials other than silicon may also be used, such as glasses orplastics. Examples include polyimide such as Kapton, polyethyleneterephthalate or Mylar-type materials, acetate, polymethylmethacrylateor other. Plastic substrates have the advantage of low cost andsimplicity of fabrication and also offering the potential for mechanicalflexibility which makes the present data storage device suitable forintegration into plastic cards such as Smart Cards, or into clothing.

Because no mechanical access is required to the surface of the presentdata storage device, as is required in compact disc, magnetic tape andmagnetic hard disk storage, a large number of substrates can be stackedon top of each other to form a 3-dimensional memory cube.

The present data storage device's areal storage density is moderate,being higher than magnetic tape but lower than magnetic hard disks.Reading and writing data rates can be very high if required, and evenhigher than hard disk drive rates. However, the present data storagedevice stores data serially in a ring, and so access time to a givenblock of data is likely to be relatively slow, making the present datastorage device of limited applicability as a direct replacement for theprimary hard disk drive in computers.

International patent application PCT/GB01/05072 describes how digitallogic circuits could be constructed from chains of nanometer scale dotsof magnetic material, or nanometer scale planar magnetic wires. Inparticular is described a magnetic NOT-gate which is shown in FIG. 1 ofthe present application.

In FIG. 1, the arrows represent magnetization direction within thenarrow strips of magnetic material which form the gate 100. The centralstructure 102 of the gate 100 reverses the direction of magnetizationcoming in from the left.

In use, the gate 100 is to be placed in a magnetic field, the vector ofwhich rotates in the plane of the device with time. While the presentdata storage device is not limited by any theory of operation, it can benoted that because of magnetic shape anisotropy, the magnetization inthe wire is generally confined to lie along the long axis of the wire.This means that there are two possible magnetization directions and sothere exists a natural binary representation. A change in magnetizationdirection is mediated by a magnetic domain wall being swept along thewire by the applied field. The fact that the applied field rotates meansthat domain walls can be carried around corners.

In accordance with examples of embodiments, a NOT-gate similar to theone described above is fabricated by a suitable method. Ideally forpresent purposes, the shape of the gate is modified slightly from thatshown in FIG. 1 to have a cycloidal shape. The output of the gate isconnected back into its input using a suitable magnetic conduit such asa planar magnetic wire to form a closed loop. An array of such loopsforms the present data storage device according to this preferredembodiment, which comprises planar magnetic nanowires formed into largeclosed loops of serially connected cycloids to form chains of magneticNOT gates. The output of the last NOT gate in each chain is fed backinto the input of the first NOT gate by a planar magnetic wire so as toform a closed loop for the data sequence to circulate around.

The cycloids serve as inversion nodes for propagating domain walls asthey propagate through the nanowires under action of a suitablerotational operating field in the manner noted above and described ingreater detail below. The inverted output only appears after a timedelay equal to one half of the period of the rotational applied field,which makes each inversion node appear as a single bit memory cell orflip-flop. Thus, the loops of cycloids have the same memory function asa serial circular shift register, and can serve as a data storage devicein accordance with examples of embodiments.

According to a further aspect of the present data storage device, a datastorage system is provided comprising one or more device elements asabove described and further comprising a magnetic field driver forproviding a controlled time-varying driving magnetic field. The magneticfield driver is preferably set up such that the driving field is appliedsimultaneously to all of the cycloids in a given loop and may be appliedsimultaneously to all of the loops in the system. This gives adistinctive feature of the present system in operation. The magneticfield is applied to the entire loop at once so that all of the data bitsadvance together, instead of only locally under the write head as wouldbe the case with conventional magnetic data storage.

Any suitable field may be envisaged. Preferably, the magnetic fielddriver provides a controlled magnetic field consisting of two orthogonalfields operating in a predetermined sequence, preferably alternating,and more preferably forming a clocking field in a clockwise oranti-clockwise direction. Using such a system, data may be stored in thestorage device(s) in accordance with the first aspect of the presentdata storage device.

The system may further comprise suitable electrical and/or data inputand/or outputs to enable the data storage device to be used in a memorystorage and retrieval system.

These as well as other aspects and advantages will become apparent tothose of ordinary skill in the art by reading the following detaileddescription, with reference where appropriate to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various examples of embodiments are described herein with reference tothe following drawings, wherein like numerals denote like entities.

FIG. 1 is a schematic representation of a prior art magnetic NOT-gate(see above);

FIG. 2 is a magnetic NOT gate modified for use as a data storage devicein accordance with examples of embodiments;

FIG. 3 is a schematic representation of the structure of the NOT gate ofFIG. 2 (Part A) and of its effect on a domain wall entering at point Punder the action of a rotating magnetic field H;

FIG. 4 shows three magnetic NOT gates connected in a ring to form a5-bit serial shift register in Part A, and Part B shows how simple(trace I) and complex (trace II) bit sequences can be forced tocirculate around the ring by the application of a rotating magneticfield (the asterisk in Part A showing the point in the loop where themeasurements shown in Part B were made);

FIG. 5 shows eleven magnetic NOT gates connected in a ring to form a13-bit serial memory in Part A, and Part B shows a simple 13-bit datasequence cycling around the loop under the action of a rotating magneticfield (the asterisk in Part A showing the point in the loop where themeasurements shown in Part B were made).

FIG. 6 is a schematic illustration of the data writing and read-outmechanism in accordance with examples of embodiments.

FIG. 7 is a schematic illustration of a number of magnetic loops on thesame substrate, addressed individually by electronic multiplexers anddemultiplexers; and

FIG. 8 is a schematic illustration of the stacking of a number ofsubstrates each containing a number of data loops to form a3-dimensional memory cube.

DETAILED DESCRIPTION OF THE DRAWINGS

An example of the operation of the present magnetic data storage devicewill now be described by way of example, with reference to FIGS. 2 to 8.

FIG. 2 shows a NOT gate 200 similar to the gate 100 of FIG. 1, butparticularly adapted to be optimized for the present data storage deviceto have a cycloidal shape. The gate 200 is made by focused ion beammilling of a 5 nm thick Permalloy (Ni₈₀Fe₂₀) film on a siliconsubstrate. Only the bright white shaded portion 202 is magneticmaterial; other contrast is due to the multi-step milling process usedduring the fabrication of the gate. FIG. 2 a shows the gate 200 with itsoutput 204 connected back to its input 206 using a planar magnetic wire208 to form a closed loop. FIG. 2 b shows a close up of the gatestructure, which has a cycloidal form. Magnetooptical measurements atpoints I and II in response to an applied rotating magnetic field areshown in FIG. 2 c. There is a half-cycle delay between the input (traceI) changing state and the output (trace II) changing state equal to onehalf of the period of the applied rotating magnetic field, whichcorresponds to a memory function.

FIG. 3 gives an explanation of the inverting action of the cycloid andin particular of the origin of this delay.

Under low magnetic field conditions, the magnetization direction withinsub-micron ferromagnetic planar wires tends to lie along the wirelong-axis due to strong magnetic shape anisotropy. When two oppositelydirected magnetizations meet within a wire, the re-alignment ofsuccessive atomic magnetic moments is not abrupt but occurs graduallyover a certain distance to form a domain wall.

It is now known that domain walls can propagate along straightsub-micron magnetic wires by application of a magnetic field parallel tothe wire. In use of the present data storage device, a magnetic field isapplied with a vector that rotates with time in the sample plane can beused to propagate domain walls along magnetic wires that also changedirection and turn corners. The clockwise or counter-clockwise rotationdefines the magnetic field chirality. A domain wall should propagatearound a magnetic wire corner providing that the field and corner are ofthe same chirality. However, the chirality of a corner depends upon thedirection of domain wall propagation so that, within a rotating magneticfield of given chirality, a domain wall will only be able to passthrough a given corner in one direction. This satisfies the importantrequirement of any logic systems that a definite signal flow directionmust exist. The two stable magnetization directions within sub-micronmagnetic wires provide a natural means of representing the two Booleanlogic states and this, together with application of a rotating magneticfield, is the basis of operation of each logical unit of the memorydevice.

The cycloid 200 illustrated in FIG. 3 provides an inverting function anddemonstrates NOT-gate functionality when within a suitable rotatingmagnetic field. Suppose the magnetic field is rotating in acounter-clockwise sense. A domain wall arriving at terminal ‘P’ (FIG.3B) of the junction will propagate around the first corner of thejunction (FIG. 3C) and through to terminal ‘Q’ as the applied fieldrotates from the horizontal to the vertical direction. The magnetizationbetween ‘P’ and ‘Q’ will now be continuous (FIG. 3D). Then, as themagnetic field vector continues to rotate towards the oppositehorizontal direction, the domain wall should propagate around the secondcorner of the junction (FIG. 3E), exiting at terminal ‘R’ and restoringcontinuous magnetization between ‘Q’ and ‘R’. The magnetization of thewire 208 immediately after the junction should now be reversed comparedwith that immediately before the junction. The junction should thereforeperform the desired NOT-function with a half field-cycle propagationdelay. This operation is analogous to a car reversing its direction byperforming a three-point turn.

There is thus a half-cycle total delay between the wall arriving at theinput 206 and leaving from the output 204. In accordance with examplesof embodiments, we identify that this synchronous delay has anassociated memory function which can be exploited by connecting a largenumber of magnetic NOT gates, such as the gate 200, together in series,and then piping the output of the chain back to the input.

FIG. 4 shows a reduced version 400 of the present data storage device inwhich three NOT gates 402, 404, and 406 have been connected in a chain408, and the output 410 of the chain 408 fed back into the beginning 412of the chain 408 by a planar magnetic wire 414. We have programmed twodifferent data bit sequences into the device 400 through a specificapplication of magnetic fields and then started to cycle the data aroundthe loop by starting the rotating magnetic field.

Trace I of FIG. 4 b shows a simple bit-sequence cycling around the chain408; the pattern repeats every 5 cycles of the rotating field. Trace IIof FIG. 4 b shows a more complex sequence cycling around the loop, witha period of 5 cycles of the rotating field. The device 400 iseffectively behaving as a 5-bit serial shift register. The data bitsequence takes one step to the right on each complete cycle of therotating field. These data were obtained using a counter-clockwiserotating field and so the data were cycling around the magnetic ring ina counter-clockwise sense. We find that reversing the rotating sense ofthe field to clockwise causes the data to reverse direction and to beginto cycle around the magnetic ring in a clockwise sense.

FIG. 5 shows a test of a version 500 of the present data storage deviceusing 11 NOT gates. FIG. 5 b shows a simple bit sequence cycling aroundthe loop with a repeat period of 13 cycles of the rotating field.

Data are written into each loop by a current-carrying lithographic wirepassing over the top or underneath the planar magnetic wire. Data areread out of each loop by using a magnetic tunnel junction attached toone part of the loop or by measuring the electrical resistance of adomain wall present at one of the corners of the wire or by measuringthe electrical resistance of a domain wall present in one of the NOTgates.

FIG. 6 shows examples of these data input/output methods. Data iswritten into the loop by a current carrying electrical lithographic wire602 which passes above or beneath the ring. Data circulates around theloop in the direction of arrow 604. Data is read out of the loop eitherby forming a magnetic tunnel junction 606 between two electricalcontacts 608 and 610 at one point of the loop (upper panel) or byapplying two electrical contacts 612 and 614 to measure the resistanceof any domain wall contained within a small part of the ring (lowerpanel).

In a variant on the present data storage device (not shown in thefigure), the magnetic conduit itself does not form a closed loop ofinversion nodes, but rather a linear chain of inversion nodes with datawriting facility at one end of the chain and data reading facility atthe other end of the chain. In this case, it is necessary for externalcontrol circuitry to feed the data back electronically from the outputof the chain to the input of the chain so that data is still able tocirculate around an apparently closed loop.

The data loops sit in a magnetic field, the vector of which rotates inthe plane of the loops with time at a frequency in the range 1 Hz-200MHz. The field magnitude may be constant as the field rotates, thusforming a circular locus for the magnetic field vector, or it may vary,thus forming an elliptical locus for the magnetic field vector. This canbe achieved in small area devices by placing an electromagnetic stripline underneath the loops and then passing an alternating currentthrough the strip line. In a larger area device, the substrate carryingthe loops is placed within a quadrapole electromagnet.

The field magnitude should be strong enough to ensure that a domain wallcan be pushed all the way through each NOT gate, but not so strong thatnew domain walls can be nucleated independently of the data inputmechanism. The field required to push a domain wall through each NOTgate can be tuned by varying the thickness of the loops, the width ofthe loops, and the magnetic material used to make the loops. This fieldshould be large enough that the device does not suffer erasure fromstray ambient magnetic fields. The present data storage device may beshielded using MuMetal if stray field erasure is a problem. An optimizeddevice will use applied field strengths in the range of 50-200 Oe.

The present data storage device may comprise a large number of dataloops on a single substrate with electronic multiplexers anddemultiplexers being used to address the correct loop, as illustrated inFIG. 7. A number of loops 702 are shown between data writing drivers andmultiplexers 704 and data reading demultiplexers and amplifiers 706.

An optimal balance between the number of loops 702 and the number of NOTgates in each loop 702 will be found for a given application. A smallnumber of loops 702 each comprising a large number of NOT gates will bevery easy and cheap to integrate into a package but will be prone tofailure of the entire device if a single NOT gate fails throughmanufacturing defects. Such a combination will also have a long dataaccess time, as one must wait a large number of clock cycles on averagefor a given data block to cycle round to the reading position. A largenumber of loops 702 each comprising a small number of NOT gates will bevery resistant to failure of individual NOT gates (the loop 702containing the failed gate can be taken out of circuit withoutsignificantly reducing the overall storage capacity) and will have arapid access time, but will involve more reading and writing points (andtherefore higher cost) and it will be more complicated to integrate alarge number of loops 702 into a single integrated circuit package. Allof the figures in this document show loops of 8 gates. This is purelyfigurative—in practice each loop will contain many thousands of gates.

A particular feature of the present data storage device is that one isnot limited to a 2-dimensional plane in placing data loops. Unlikecompact disc, magnetic tape, and magnetic hard disk storage, nomechanical access is required to the surface of the present data storagedevice. Substrates 802 may be placed on top of each other to form a3-dimensional data cube 800, as shown in FIG. 8. This has the advantageof allowing much higher data storage densities to be achieved. Ifdesired, all of the substrates 802 in a cube 800 may share the sameapplied rotating magnetic field, thus keeping the layers insynchronization with each other and reducing the complexity of thedevice.

The present data storage device may be configured to input/output asingle serial stream of data, or if desired, streams of data words ofmultiple bit width may stored by using several rings or layers inparallel.

Because of the low access time, the present data storage device is notsuitable as a replacement for the primary hard disk in computers. Itmay, however, find application in some of the following situations, aswell as others.

-   -   Temporary storage of digital music for pocket digital audio        players such as MP3 players. This application requires low-cost,        non-volatile, re-writable storage of digital information which        is usually replayed serially. Using 200 nm-wide planar wires, a        NOT gate would occupy an area of 1 μm². A 1 cm² single layer        covered with data chains would therefore provide 12 Mbytes of        serial data storage, which is sufficient for 12 minutes of        CD-quality music. Stacking of layers will provide several hours        of CD-quality audio at very low cost.    -   Temporary storage of digital photographs in digital cameras.        This function is accomplished currently by FLASH electronic        memory, which is expensive and which has a limited number of        re-write cycles.    -   Non-volatile offline storage for mobile phones, personal        organizers, palm top computers, and SMART cards.

Various examples of embodiments have been described above. Those skilledin the art will understand, however, that changes and modifications maybe made to those examples without departing from the scope of theclaims.

1. A data storage device for storing digital information in a readableform comprises one or more memory elements, each memory elementcomprising a planar magnetic conduit capable of sustaining andpropagating a magnetic domain wall formed into a continuous propagationtrack, wherein each continuous track is provided with at least oneinversion node whereat the magnetization direction of a domain wallpropagating along the conduit under action of an applied field ischanged, each inversion node comprising a portion in which a directionchange away from an initial path and a subsequent direction change backto the initial path are provided in the conduit such that no directpropagation path is possible across a deviating portion.
 2. The datastorage device of claim 1 wherein each continuous track is provided withat least one inversion node whereat the magnetization direction of adomain wall propagating along the conduit under action of a suitableapplied field is substantially reversed.
 3. The data storage device ofclaim 1 wherein each continuous track is provided with a large pluralityof inversion nodes.
 4. The data storage device of claim 2 wherein eachcontinuous track is provided with a large plurality of inversion nodes.5. The data storage device of claim 1 wherein a conduit is formed into aclosed loop to comprise a continuous propagation track.
 6. The datastorage device of claim 2 wherein a conduit is formed into a closed loopto comprise a continuous propagation track.
 7. The data storage deviceof claim 3 wherein a conduit is formed into a closed loop to comprise acontinuous propagation track.
 8. The data storage device of claim 1wherein a conduit does not form an entire closed loop but a chain ofinversion nodes, and means are provided to transfer data between the twoends thereof so that data is still able to circulate around anapparently closed loop, the means comprising a data writing facility atone end of the chain and data reading facility at the other end of thechain, and additional circuitry to feed the data back electronicallyfrom the output of the chain to the input of the chain.
 9. The datastorage device of claim 1 wherein deviations comprise 90° deviationsfrom the initial path of the conduit.
 10. The data storage device ofclaim 1 wherein deviations from the initial path occur gradually over adistance along the conduit track.
 11. The data storage device of claim 1wherein the inversion node comprises a cycloidal portion within aconduit loop structure or a topological equivalent of such a structure.12. The data storage device of claim 11 comprising a plurality of suchcycloidal portions provided in each loop.
 13. The data storage device ofclaim 12 comprising a number of magnetic conduits formed into closedloops each comprising a plurality of cycloids serving to effect abruptdirectional reversals in a magnetization direction of a domain wallpassing thereacross.
 14. The data storage device of claim 13 whereineach cycloid has a turning radius which is in the range three to tentimes the conduit width.
 15. The data storage device of claim 1 whereinthe magnetic conduit comprises a particular generally planar magneticwire on a suitable substrate.
 16. The data storage device of claim 15wherein the magnetic wire comprises a magnetic nanowire with a thicknessof between 2 nm and 25 nm and a width of between 50 nm and 1 μm.